Recently, various devices, such as industrial machinery, household appliances, and vehicles, using a high voltage battery have emerged, and particularly, a high voltage battery has been more actively used in a vehicle technical field.
A vehicle using an internal combustion engine that uses fossil fuel, such as gasoline or heavy oil, as main fuel severely influences generation of pollution, such as atmospheric pollution. Therefore, recently, in order to decrease the generation of pollution, a lot of efforts is made to develop an electric vehicle (EV) or a hybrid vehicle.
The EV refers to a vehicle which does not use oil fuel and an engine, but uses an electric battery and an electric motor. That is, an EV which drives a vehicle by rotating a motor with electricity accumulated in a battery is developed before a gasoline vehicle, but the EV was not commercialized due to problems, such as a heavy battery and a charging time. However, as the energy and environment problems are recently getting serious, research on commercialization of the EV begins from 1990s.
In the meantime, recently, as a battery technology is remarkably developed, an EV and a hybrid electric vehicle (HEV) adaptively using fossil fuel and electric energy have been commercialized.
Since the HEV uses both gasoline and electricity as a power source, the HEV receives positive reviews in an aspect of improvement of fuel efficiency and a decrease in exhaust gas. In a case of the HEV, it is a matter of overcoming a difference in a price between the HEV and a gasoline vehicle, and the amount of secondary batteries mounted may be decreased to a level of ⅓ of that of the EV, so that it is expected that the HEV may serve a transitional role in evolving into a complete EV.
The HEV and the EV using electric energy use a battery, in which a plurality of chargeable/dischargeable secondary cells is formed in the form of one pack, as a main power source, so that the HEV and the EV have advantages in that no exhaust gas and very little noise are generated.
As described above, in the vehicle using electric energy, battery performance directly influences performance of the vehicle, so that a battery management system (BMS), which is capable of efficiently managing charging/discharging of each battery cell by measuring a voltage of each battery cell and a voltage, a current, and the like of the entire batteries, and is capable of stably controlling a corresponding cell by monitoring a state of a cell sensing IC that senses each battery cell, is required.
In the meantime, a form of the BMS is changed according to a structure of the battery. In this case, unlike a general HEV, a plug-in HEV includes a high voltage charging system, as well as a high voltage battery system, so that a space, in which a battery is mountable, is limited. Accordingly, in the PHEV, the entire battery cells are divided into a master battery and a slave battery and are mounted at different positions in the vehicle. In this case, the BMS may be formed of a master BMS that manages a master battery and a slave BMS that manages a slave battery.
In the master BMS and the slave BMS, the master BMS controls a charging/discharging state of the master battery and controls on/off of a main relay that connects the battery and a motor of the vehicle. Further, the slave BMS controls a charging/discharging state of the slave battery and controls on/off of a charging relay that connects the battery and a charger. That is, the master BMS and the slave BMS are independently operated.
Accordingly, when the master battery is over-charged during charging of the battery, the master BMS may turn off the main relay to prevent an over-current from flowing into the motor of the vehicle, but the master BMS cannot control the charging relay, so that there is a problem in that it is impossible to prevent the mater battery from being continuously over-charged.